If you are running SmarterMail via virtualization on a Hyper-V or VMware host then Veeam Backup is the hands-down best solution. For a physical server I'd choose Macrium Server for image based backup offering great "bare metal" restore options. Also, if you have or are considering a Synology NAS, it includes some good backup software options, too.

If you run it on VmWare clone it via a scheduled task every 24 hrs. Much better than Veeam and free.

We have used both Veeam and Synology's Active Backup. Both work excellent, Synology's is free if you have one of their NAS's.
If you want free, Veeam Agent is their free client software that can run at least on Windows machines. Not sure about linux as I haven't tried it, but the client works very well and will backup to whatever target you wish.

+1 for Veeam. It's quick, easy, and works natively with Windows/Hyper-V!

Veeam or Altaro VM Backup

Veeam.
It has many free solutions:
- Veeam Backup&Recovery Community Edition for Hyper-V/vmWare (and soon for ProxmoxVE) for a maximum of 10 VMs
- Veeam Agent free for Windows/Linux "bare metal" (even in a VM) single server solution

Nothing out there is better.

TrueNAS - Open Source, does time based snapshots and can do full replication to other TrueNAS servers.

I am using Acronis Cyber Cloud and attaching it via a local backup storage target.